Flumazenil

Flumazenil (also known as flumazepil, code name Ro 15-1788) is a selective GABAAantagonist[1] administered via injection or intranasally. Therapeutically, it acts as both an antagonist and antidote to benzodiazepines (particularly in cases of overdose), through competitive inhibition.

It was first characterized in 1981,[2] and was first marketed in 1987 by Hoffmann-La Roche under the trade name Anexate. However, it did not receive FDA approval December 20, 1991. The developer lost its exclusive patent rights in 2008; so at present, generic formulations of this drug are available. Intravenous flumazenil is primarily used to treat benzodiazepine overdoses and to help reverse anesthesia. Administration of flumazenil by sublingual lozenge and topical cream has also been tested.[3][4]

Contents

The drug has been used as an antidote in the treatment of benzodiazepine overdoses.[5] It reverses the effects of benzodiazepines by competitive inhibition at the GABAA binding site of benzodiazepine receptors, which are present through about 70% of the body. There are many complications that must be taken into consideration when used in the acute care setting.[5] These include lowered seizure threshold, agitation, and anxiousness. Flumazenil's short half-life requires multiple doses. Because of the potential risks of withdrawal symptoms and the drug's short half-life, patients must be carefully monitorered to prevent recurrence of overdose symptoms or adverse side effects.

Flumazenil is also sometimes used after surgery to reverse the sedative effects of benzodiazepines. This is similar to naloxone's application to reverse the effect of opiates and opioids following surgery. Administration of the drug requires careful monitoring by an anesthesiologist due to potential side effects and serious risks associated with over-administeration. Likewise, post-surgical monitoring is also necessary because flumazenil can mask the apparent metabolization ("wearing off") of the drug after removal of patient life-support and monitoring equipment.

Flumazenil has been effectively used to treat overdoses of non-benzodiazepine hypnotics, such as zolpidem, zaleplon and zopiclone (also known as "Z-drugs").[6]

The drug has also been used in hepatic encephalopathy. It may have beneficial short‐term effects in people with cirrhosis, but there is no evidence for long-term benefits.[8]

The onset of action is rapid, and effects are usually seen within one to two minutes. The peak effect is seen at six to ten minutes. The recommended dose for adults is 200 μg every 1–2 minutes until the effect is seen, up to a maximum of 3 mg per hour. It is available as a clear, colourless solution for intravenous injection, containing 500 μg in 5 mL.

Many benzodiazepines (including midazolam) have longer half-lives than flumazenil. Therefore, in cases of overdose, repeat doses of flumazenil may be required to prevent recurrent symptoms once the initial dose of flumazenil wears off.

It is hepatically metabolised to inactive compounds which are excreted in the urine. Individuals who are physically dependent on benzodiazepines may suffer benzodiazepine withdrawal symptoms, including seizure, upon rapid administration of flumazenil.

In terms of drug enforcement initiatives, diversion control programs and required post-marketing surveillence of adverse events, orders for flumazenil may trigger a prescription audit to the search for benzodiazepine misuse and for clinically significant adverse reactions related to their use.[10]

In Italy, the gold standard for treatment of high-dose benzodiazepine dependency is 8–10 days of low-dose, slowly infused flumazenil.[12] One addiction treatment centre in Italy has used flumazenil to treat over 300 patients who were dependent on high doses of benzodiazepines (up to 70 times higher than conventionally prescribed) with physicians being among the clinic's most common patients.[13]

Epileptic patients who have become tolerant to the anti-seizure effects of the benzodiazepine clonazepam became seizure-free for several days after treatment with 1.5 mg of flumazenil.[14] Similarly, patients who were dependent on high doses of benzodiazepines (median dosage 333 mg diazepam-equivalent) were able to be stabilised on a low dose of clonazepam after 7–8 days of treatment with flumazenil.[15]

Flumazenil has been tested against placebo in benzo-dependent subjects. Results showed that typical benzodiazepine withdrawal effects were reversed with few to no symptoms.[16] Flumazenil was also shown to produce significantly fewer withdrawal symptoms than saline in a randomized, placebo-controlled study with benzodiazepine-dependent subjects. Additionally, relapse rates were much lower during subsequent follow-up.[17]

In vitro studies of tissue cultured cell lines have shown that chronic treatment with flumazenil enhanced the benzodiazepine binding site where such receptors have become more numerous and uncoupling/down-regulation of GABAA has been reversed.[18][19][20] After long-term exposure to benzodiazepines, GABAA receptors become down-regulated and uncoupled. Growth of new receptors and recoupling after prolonged flumazenil exposure has also been observed. It is thought this may be due to increased synthesis of receptor proteins.[21]

Flumazenil was found to be more effective than placebo in reducing feelings of hostility and aggression in patients who had been free of benzodiazepines for 4–266 weeks.[22] This may suggest a role for flumazenil in treating protracted benzodiazepine withdrawal symptoms.

Low-dose, slow subcutaneous flumazenil administration is a safe procedure for patients withdrawing from long-term, high-dose benzodiazepine dependency.[23] It has a low risk of seizures even amongst those who have experienced convulsions when previously attempting benzodiazepine withdrawal.[24]

Flumazenil, an imidazobenzodiazepine derivative, antagonizes the actions of benzodiazepines on the central nervous system. Flumazenil competitively inhibits the activity at the benzodiazepine recognition site on the GABA/benzodiazepine receptor complex. Because the body does not produce endogenous benzodiazepines, flumazenil only creates behavioral effects when administered concurrently with a benzodiazepine receptor agonist or inverse agonist.[citation needed]

Flumazenil does not antagonize all of the central nervous system effects of drugs affecting GABA-ergic neurons by means other than the benzodiazepine receptor (including ethanol, barbiturates, or general anesthetics) and does not reverse the effects of opioids.